L-Calcineurin is an important regulatory enzyme that functions in many cellular processes including T cell signal transduction. Drug such as cyclosporin and FK506 that inhibit calcineurin (CIs) are clinically useful to suppress the immune system following organ transplantation. Unfortunately, inhibition of calcineurin also affects tissues other than the immune system and long-term use of CIs often produces therapeutically-limiting side-effects including nephrotoxicity and cardiovascular disease. Work in our laboratory is focused on specificity of calcineurin action in the kidney. Interestingly, when we examined mice that lack the alpha isoform of the catalytic subunit of calcineurin and mice that lack the beta isoform, we find very different effects. Namely, loss off alpha severely impairs development of the kidney, alters cell cycle regulation, and results in increased matrix production - features consistent with Cl nephrotoxicity while mice lacking the beta isoform lack signs of significant renal damage. Moreover, we find that alpha-/- mice develop hyperlipidemia, demonstrating a direct connection between calcineurin action and development of cardiovascular disease. Finally, mice lacking the beta isoform have been previously described to have an "immune-suppressed"-like phenotype while T cell function in alpha null animals can still be suppressed with cyclosporin. These mouse models clearly demonstrate that calcineurin isoforms have distinct functions that are particularly relevant in the transplant setting. Inhibition of the alpha isoform produces nephrotoxicity and hyperlipidemia while inhibition of the beta isoform results in suppression of T cell signaling. Therefore, we hypothesize that selective inhibition of the beta isoform will result in immune suppression with fewer toxic side-effects. To test this hypothesis, it will be necessary to generate a mouse model that will allow us to carefully compare the effects of selective loss of calcineurin isoforms. Since alpha-/- mice live only a few weeks, it is not currently possible to perform such studies. However, recent advances in gene manipulations provide innovative tools to generate inducible, isoform-specific knockout mice. We will create these mice and characterize the effect of inducible loss of each isoform in immune suppression and nephrotoxic / cardio- vascular side- effects. Using a well-characterized skin transplant model, we will then test the hypothesis that selective inhibition of calcineurin isoforms results in immune suppression with fewer side-effects. [unreadable] [unreadable] [unreadable]